MARCH2 regulates autophagy by promoting CFTR ubiquitination and degradation and PIK3CA-AKT-MTOR signaling

MARCH2 (membrane-associated RING-CH protein 2), an E3 ubiquitin ligase, is mainly associated with the vesicle trafficking. In the present study, for the first time, we demonstrated that MARCH2 negatively regulates autophagy. Our data indicated that overexpression of MARCH2 impaired autophagy, as evidenced by attenuated levels of LC3B-II and impaired degradation of endogenous and exogenous autophagic substrates. By contrast, loss of MARCH2 expression had the opposite effects. In vivo experiments demonstrate that MARCH2 knockout mediated autophagy results in an inhibition of tumorigenicity. Further investigation revealed that the induction of autophagy by MARCH2 deficiency was mediated through the PIK3CA-AKT-MTOR signaling pathway. Additionally, we found that MARCH2 interacts with CFTR (cystic fibrosis transmembrane conductance regulator), promotes the ubiquitination and degradation of CFTR, and inhibits CFTR-mediated autophagy in tumor cells. The functional PDZ domain of MARCH2 is required for the association with CFTR. Thus, our study identified a novel negative regulator of autophagy and suggested that the physical and functional connection between the MARCH2 and CFTR in different conditions will be elucidated in the further experiments.MARCH2（膜相关RING-CH蛋白2，membrane-associated RING-CH protein 2）作为一种E3泛素连接酶（E3 ubiquitin ligase），主要参与囊泡运输过程。本研究首次证实，MARCH2可负向调控自噬（autophagy）。研究数据显示，MARCH2过表达会损伤自噬功能，具体表现为LC3B-II水平下调以及内源性、外源性自噬底物的降解受阻。与之相反，MARCH2表达缺失则会产生完全相反的生物学效应。体内实验证实，MARCH2基因敲除介导的自噬可抑制肿瘤致瘤性。进一步机制研究发现，MARCH2缺失所诱导的自噬是通过PIK3CA-AKT-MTOR信号通路介导的。此外，本研究还发现MARCH2可与囊性纤维化跨膜电导调节因子（CFTR, cystic fibrosis transmembrane conductance regulator）发生相互作用，促进CFTR的泛素化修饰与降解，并在肿瘤细胞中抑制CFTR介导的自噬。MARCH2的功能性PDZ结构域是其与CFTR结合的必要条件。综上，本研究鉴定出一种全新的自噬负调控因子，并指出未来实验将进一步阐明不同条件下MARCH2与CFTR之间的物理相互作用与功能关联。